Traditional vaccination with immunogenic proteins has eliminated or reduced the incidence of many diseases in the last century, however there are problems involved in using proteins associated with certain pathogens and disease states. Immunization by genes encoding immunogens, rather than with the immunogen itself, has opened up new possibilities for vaccine research and development and offers chances for new applications and indications for future vaccines. For example, in numerous animal models, DNA immunization has been shown to induce protective immunity against infectious diseases (viral, bacterial and protozoan). Recent examples include DNA vaccine for prophylactic or therapeutic immunization against hepatitis B virus (Davis (1999) Mt Sinai J Med. 66: 84-90). Other applications of DNA vaccine technology include the treatment of cancer as well as auto-immune disease. For example, DNA vaccines encoding prostate specific antigen (PSA) have been developed to treat prostate cancer (see e.g. Kim et al. (2001) Oncogene 20: 4497-506). Furthermore, DNA vaccine technology has applications in treating autoimmune disease, where the immune system attacks the hosts own tissues, resulting in diseases such as myasthenia gravis, diabetes or multiple sclerosis. Autoimmune disease results from a breakdown in tolerance to self antigens; however the same fundamental immunological reactions that control immune responses to foreign antigens also operate in autoimmune diseases (see e.g. Ramshaw et al. (1997) Immunol Cell Biol 75: 409-13). Accordingly, DNA vaccine technology can be used to re-establish tolerance to self antigens as well as to establish tolerance to environmental immunogens where desirable.
These DNA vaccine strategies exploit the underlying mechanisms of antigen processing, immune presentation and regulation of immune responses in order to optimize the prophylactic or therapeutic value of the vaccine, particularly for vaccines against chronic or persistent infectious diseases and tumors. DNA technology has facilitated the rapid development of plasmid-based vaccines designed to prevent viral, bacterial and parasitic infections. Current DNA vaccination strategies address: the construction of specialized vaccine plasmids; screening for protective immunogens to be encoded by these plasmids; optimization of the mode of application; analysis of vaccine pharmacokinetics; as well as analysis of vaccine safety and immunotoxicology. DNA vaccines have the potential to accelerate the research phase of new vaccines and to improve the chances of success, since finding new immunogens with the desired properties requires less effort than for conventional vaccines. However, on the way to successful DNA vaccines, several limitations must be dealt with including: the persistence and distribution of inoculated plasmid DNA in vivo; its potential to express antigens inappropriately; and the potentially deleterious ability to insert genes into the host cell's genome. Patents directed toward and describing such DNA vaccine technology include U.S. Pat. Nos. 5,589,466; 5,738,852; 5,925,362; 6,130,052; 6,149,906; 6,214,804; 6,224,870; 6,245,525; and 6,294,378, the contents of which are incorporated herein by reference.
The initiation of T cell-dependent immune responses depends on presentation of antigens by bone marrow derived antigen-presenting cells (APCs) such as dendritic cells. Tolerance induction also depends on the expression of antigens by tolerizing antigen presenting cells. Immunotherapy approaches are aimed at introducing antigen into various populations of APCs such as dendritic cells. However, the efficiency with which standard immunotherapy and vaccine approaches introduces antigens into APCs is relatively low. Standard vaccines appear to introduce antigen into relatively small numbers of APCs in the body. Ex vivo transduction or loading of dendritic cells followed by their reinfusion can increase the number of antigen-loaded APCs—however, the ex vivo manipulation and maturation of DCs appears to interfere with their ability to stimulate T cell responses subsequent to reintroduction into the body. A second problem solved relates to the importance of activating APCs with the appropriate signals. Current approaches utilize reagents provided systemically which have many side effects due to their activity on many different cell types. Accordingly, it would be desirable to have methods and compositions for the effective expression of antigens in large numbers of bone marrow derived APCs as well as to effect efficient immune responses to these APCs while avoiding undesirable side effects resulting from strategies employing systemic administration of immunostimulatory reagents.